Electrically driven vehicle steered by control of power and speed of tractive elements

ABSTRACT

The wheels of a vehicle are driven by inductor type synchronous motors having solid rotors without windings and commutators. A diesel on the vehicle drives a pair of high frequency rotating generators each of which supplies power to a pair of the synchronous motors. Power pedal means actuated by the operator derive a power signal proportional to the desired tractive effort for the vehicle. A separate electric drive for each motor includes means for deriving a control signal modulated at motor speed, a cycloconverter between each motor and its generator regulated by the control signal, tachometer means for deriving a speed signal which is a function of motor speed, and control means responsive to both the power signal and speed signal for regulating the magnitude and phase of the control signal so that the motor output power is constant over the speed range at a level in accordance with the power pedal setting. Brake means actuated by the operator derive a brake signal, and the vehicle has means for shifting the phase of the control signals for all the motors to regeneratively brake them when the brake signal exceeds the power signal. The vehicle has travel direction selector means for shifting the phase of all the control signals to reverse the direction of motor rotation and thus propel the vehicle backward. The vehicle has manually operated means for setting a speed limit for the vehicle and means for deriving a speed limit signal which is additive to the brake signal to regeneratively brake the motors when vehicle speed exceeds the set speed limit. Turn compensation means increase the power supplied to the motors of the wheels on the outside of a turn and decrease the power supplied to the motors of the wheels on the inside of the turn as a function of the degree of turn and the magnitude of the power signal.

United States tet Ringland et a1.

[Ill 3,720,863

H lMarch 13, 1973 ELECTRHCALLY DRHVEN VEHHCLE STEERED BY CONTROL OF WOWER AND SPEED OF TRACTHVE ELEMENTS [73] Assignee: Allis-Chalmers Corporation, Milwaukee, Wis.

[22] Filed: Nov. 19, 1970 [21] Appl. No; 91,115

Related [1.8. Application Data [60] Division of Ser. No. 853,462, Aug. 27, 1969, Pat. No. 3,577,050, which is a continuation-in-part of Ser. No.

824,223, May 13, 1969.

The wheels of a vehicle are driven by inductor type synchronous motors having solid rotors without windings and commutators. A diesel on the vehicle drives a pair of high frequency rotating generators each of which supplies power to a pair of the synchronous motors. Power pedal means actuated by the operator derive a power signal proportional to the desired tractive effort for the vehicle. A separate electric drive for each motor includes means for deriving a control signal modulated at motor speed, a cycloconverter between each motor and its generator regulated by the control signal, tachometer means for deriving a speed signal which is a function of motor speed, and control means responsive to both the power signal and speed signal for regulating the magnitude and phase of the control signal so that the motor output power is constant over the speed range at a level in accordance with the power pedal setting.

ABSTRACT Brake means actuated by the operator derive a brake signal, and the vehicle has means for shifting the phase of the control signals for all the motors to regenera- [52] 11.8. CI. ..318/52, 318/67, 318/68, tively brake them when the brake signal exceeds the 318/227 power signal. The vehicle has travel direction selector [51] lint. Cl. ..1102p 7/74 means for shifting the phase of all the control signals to reverse the direction of motor rotation and thus [58] Field of Search ..318/52, 55, 58,59, 60, 67, p p the vehicle backward The Vehicle has manually operated means for setting a speed limit for the vehicle and means for deriving a speed limit signal [56] References Cmd which is additive to the brake signal to regeneratively brake 11:16 motors when vehicle speed exceeds the set speed limit. Turn compensation means increase the 3,596,154 7/1971 Gurwicz ..318/52 power supplied to the motors of the wheels on the out- 2,735,090 2/195 P X side of a turn and decrease the power supplied to the 2,962,642 HH9150 Brim? l "318/67 X motors of the wheels on the inside of the turn as a $600,655 8/1971 Karlm-w "318/67 function of the degree of turn and the magnitude of 2,407,521 9/1946 Palley ..318/52 X the power signal.

Primary ExaminerT. E. Lynch 13 Claims, 34 Drawing Figures Attorney-Lee 1-1. Kaiser et a1 f a f a: f #45727? i morn 770 f 5371 6 flfi/Vf/P I 41 CONT/70L L0 OPE/F4722 I #5411147/0 pan/m g comma; c/rrcu/r ea Pfflfll 45 1 554/50 25 i l CONTROL amt/r: I P50" I #544) Ila 40am r.

: c/Acu/r ZIFT FIN? Wl/IIA EZICT/F/C DRIVE PAIENTEDMAR 13 ms SHEET OlUF 14 e mwmw PATENTEDMAR 13 1975 SHEET 030F1 1 PATENTEDHAR 13 I975 SHEET OSUF i4 PATENTEDMAR 13 um SHEET CBUF 14 PATENTEUMAR 13 1975 SHEET U70F14 W QER PATENTEUMAR13 I973 SHEET O9UF14 PATENTEHMAR 13 ms 3, 720. 863

SHEET 10 or 14 5W OWOQOOOQQQ HEET 13UF 14 PATENTEUMAR 13 I975 ELECTRICALLY DRIVEN VEHICLE STEERED BY CONTROL OF POWER AND SPEED OF TRACTIVE ELEMENTS This application is a division of our application Ser. No. 853,462, filed Aug. 27, I969 entitled Vehicle Driven By Synchronous Motors which is a continuation-in-part of our parent application Ser. No. 824,223, entitled Vehicle Electric Motor Drive System", filed May 13, 1969 and having the same assignee as this application.

This invention relates to electrically driven vehicles and in particular to vehicles driven by synchronous electric motors.

Electrically driven vehicles may employ a diesel, gasoline, or turbine engine as the primary source of power, or prime mover. The prime mover may drive one or more generators which, in turn, power one or moreelectric motors connected to the wheels or tracks of the vehicle. On wheeled vehicles it is often advantageous to utilize a separate motor for each wheel. An electric control may be interposed between the engine-driven generatorsand the motors of such a vehicle to regulate the application of electrical power to the motors and wheels.

In the past, most electrically driven vehicles have utilized direct current electrical apparatus. Direct current motors, particularly those of the series types, are readily adaptable to electric drive systems because of their case of control, and further the electrical controls for direct current motors and generators are simple and well developed. However, the commutators and rotating armature coils required by direct current machines add to their manufacturing and maintenance cost.

Electrically driven vehicles are known which employ alternating current motors that are simple and reliable in construction. However, since the speed of an alternating current motor is determined by the frequency of the alternating current source, a control must be provided to convert the fixed frequency of the source to the required motor frequency which varies with speed.

The simplest type of alternating current motor is the induction motor, but the differential, or slip, between the speed of the rotor and that of the rotating stator field presents difficulties in using a frequency detector driven by the motor shaft for controlling the frequency converter which supplies the variable frequency to the motor stator. The stator frequency must be higher than the detected rotor frequency by the amount of the slip frequency, and further the slip results in heat losses in the rotor which are difficult to remove, particularly at low speeds. The torque of an induction motor is proportional to the square of the voltage-to-frequency ratio applied to the stator winding. For constant power and constant rpm slip conditions, the voltage applied to an induction motor over a desired speed range must increase as the square root of the applied frequency. In a typical instant of 16 to 1 frequency (and motor speed) range at constant power, the maximum supplied voltage required is four times the minimum voltage. In-

asmuch as the size of the power supply in a drive I Because the speed of a synchronous motor is inherently proportional to applied frequency, synchronous motors have generally been employed in constant speed drive systems where the motor is energized from a constant frequency source such as a 60 cycle per second power line. When energized at this frequency, the torque of a synchronous motor assumes a level sufficient to cause the motor to drive the load in synchronism with the rotating stator field. Such conventional synchronous motor operation is one of con stant speed, variable power due to the variable motor torque.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic diagram in block form of the electric drive system of a vehicle embodying the invention;

FIG. 2 is a sectional view through a vehicle wheel and the electric motor which drives it in the embodiment of FIG. ll;

FIG. 3 is an exploded perspective view of the electric motor and the angle sensor driven by it in the embodi ment of FIGS. I and 2, the motor stator and windings being shown as encapsulated in resin;

FIG. 4 is a partial front view showing the rotor and stator of the angle sensor;

FIG. 5 is a graph plotting relative torque provided by the electric drive system versus relative speed;

FIG. 6 is a graph showing the no-load saturation curve and the rated armature current, zero power factor saturation curve for the electric motor of the embodiment of FIGS. ll-S;

FIG. 7a shows the simplified equivalent circuit of the electric motor; FIG. 7b shows its vector diagram for motor operation; and, FIG. 7c shows its vector diagram for generator operation;

FIG. 8 is a graph plotting motor terminal voltage and displacement angle versus speed required to provide maximum rated power over the speed range;

FIG. 9 is a development of the angle sensor stator and rotor and also schematically illustrates the instantaneous voltages generated in the angle sensor secondary windings; i

. FIGS. 10a and 10b are schematic diagrams illustrating vector addition of the two input signals to the angle sensor primary windings to derive the output signal which controls the cycloconverter;

FIG. 11 is a graph plotting the motor and angle sensor voltages versus motor speed required to obtain constant 50 percent and percent'maximum power over the speed range;

FIG. 12 is a schematic diagram in block form of the angle sensor control, the discriminator, and the clipping circuit;

FIG. 13 is a schematic circuit diagram of the function generators of the angle sensor control;

FIG. 14 is a schematic circuit diagram of the cycloconverter and filter and showing the firing circuit in block form;

FIGS. through 15h schematically illustrate voltages in the cycloconverter of the electric drive system;

' FIG. 16 is a schematic circuit diagram of the tachometer;

FIG. 17a is a schematic circuit diagram, partially in block form, of the firing circuit for the controlled rectifiers of the cycloconverter; and FIGS. 17!; through 17] show signals at various points within the firing circuit of FIG. 17a;

FIG. 18 is a simplified schematic diagram of the relay logic circuit and the motor control;

FIG. 19 is a graph plotting the output voltage VR from current control amplifier versus motor speed;

FIG. 20 is a graph plotting motor field current versus power pedal position to provide constant power over the speed range for a selected power level;

FIG. 21 shows curves plotting as polar coordinates the variation of motor terminal voltage VT and displacement angle DT with motor speed illustrated in FIG. 8;

FIG. 22 is a schematic circuit diagram of the turn compensation means; and

FIG. 23 is a schematic circuit diagram of the speed limit circuit.

GENERAL DESCRIPTION Referring to FIG. 1, a vehicle embodying the invention has an electric drive system which provides motive power to the right front, left front, right rear and left rear wheels 12, 14, 16 and 18 of the vehicle, respectively. A prime mover on the vehicle is preferably a hydrocarbon-fueled engine such as a gas turbine or a diesel engine which operates at substantially constant speed, as determined by the setting of its governor, and is capable of providing constant power input to electric drive system 10 under all conditions of vehicle operation.

Electric drive system 10 preferably includes four electric controls, or drives 22, 24, 26 and 28 (shown in block form) for the wheels l2, l4, l6 and 18 respectively. All four drives are substantially identical, and only drive 22 for right front wheel 12 will be described.

Prime mover 20 drives a first generator 30 which provides electrical power for electric drives 22 and 24 that operate front wheels 12 and 14 and also drives a second generator 32 which provides electrical power for electric drives 26 and 28 which operate the vehicle rear wheels 16 and 18. Generators 30 and 32 are similar and may be conventional high frequency polyphase alternators, and only generator 30 will be described. Generator 30 preferably has a stationary exciting coil 34 energized from a suitable power supply (not shown) and three Wye-connected armature windings 36A, 36B and 36C which generate threephase alternating current voltages A, B and C in high frequency, constant power buses 38A, 38B and 38C respectively. Prime mover 20 runs at nearly constant speed so that the input power to electric drive system 10 and the frequency of the alternating current generated by generators 30'and 32 are nearly constant.

The input signals to electric drives 22, 24, 26 and 28 which control the transmission of power from generators 30 and 32 to vehicle wheels 12, l4, l6 and 18 are preferably derived from conventional driver-operated vehicle controlling apparatus including a steering wheel 40, a travel direction and speed limit selector 42, a power pedal 44, and a brake pedal 46 which are coupled through a master driver-operated control circuit 48 to electric drives 22, 24, 26 and 28.

Electric drive 22 includes a synchronous motor 50 which preferably is of the inductor type and has a rotor 52 mechanically coupled to right front wheel 12 through appropriate gearing (shown in FIG. 2), a threephase armature winding, or stator winding 54, and a field winding 56 mounted on the motor stator. Electric drive 22 converts the constant frequency, constant voltage output of high frequency generator 30 to a variable frequency, variable voltage, variable phase alternating current for application to armature winding 54 to regulate the torque and speed of synchronous motor 50.

Electric drive system 10 transmits the constant power output of prime mover 20 to the vehicle wheels 12, 14, 16 and 18 over a wide range of speed. The hyperbolic torque versus speed characteristic of electric drive system 10 to accomplish such transmission of constant power from prime mover 20 to the vehicle wheels over a speed range of 15 to l is shown in FIG. 5. Torque and speed are conveniently related for purpose of description to base values taken at the minimum speed at which constant maximum power is transmitted. The base rating of electric drive system 10 wherein relative torque is arbitrarily designated 1.0 and relative speed designated 1.0 is shown in FIG. 5 wherein the full line curve corresponds to the maximum power capability of diesel engine 20 with power pedal 44 fully depressed and with total power equally divided between the individual wheel drives 22, 24, 26 and 28. However, drive system 10 includes means described hereinafter to reduce motor torque under operating conditions requiring less than rated power as represented by the dotted line curve designated reduced power in FIG. 5. Vehicle speed, motor speed, and motor frequency are all directly proportional because of the use of synchronous motors 50 and the fixed ratio gearing between motors 50 and wheels 12, l4, l6 and 18. Further, motor torque and vehicle tractive effort are also directly proportional because of such fixed ratio gearing.

In the preferred embodiment of the invention motor 50 is of the synchronous inductor type, although any type synchronous motor having adjustable field excitation, including the conventional salient pole type, may be used in electric drive system 10. The conventional saturation curves of synchronous motors are commonly used to show the relationship between stator terminal voltage VT and field current I, for various load conditions. Since synchronous motors are usually operated at constant speed corresponding to a terminal voltage having a fixed frequency of 60 cycles per second, such saturation curves are usually shown for a fixed frequency. The effect of armature resistance on these synchronous motor characteristics is usually small but becomes increasingly significant as the frequency approaches zero.

When synchronous motor 50 is operated at variable frequency, as in electric drive system 10, more meaningful saturation curves which illustrate the effects of frequency variation and armature resistance at low speeds can be derived by replacing the terminal voltage VT by the variable (VT I,,R,,)/F as illustrated in FIG. 6 which shows the no-load saturation curve and the rated armature current, zero power factor saturation curve for a typical synchronous motor 50 suitable for electric drive system 10 and where:

VT is the motor terminal voltage;

1 is the armature current;

R,, is the effective armature resistance; and

F is the frequency.

It will be noted that the values shown in FIG. 6 are expressed as per unit quantities relative to the base rating of the motor. p I

The vector quantity VT I lR, is an internal voltage, commonly called the voltage behind the resistance, and represents the vector sum of the terminal voltage and the armature resistance drop, observing the appropriate phase angle between the two vectors. Commonly used convention considers the power component of armature current to be positive for generator operation and negative for motor operation. Therefore, for motor operation the vector V T I R is less than VT for power factors in the normal operating range near unity where VT and I,, are displaced approximately 180 (see FIG. 7b). The total quantity (VT+I,,R,,)/F is proportional to the net magnetic flux linking the armature winding of motor 50, which net magnetic flux is the resultant of that generated by the armature winding 54 and field winding 56.

The saturation curves of FIG. 6 permit close approximation, by well known methods, of the field current 1, corresponding to any load condition. In the preferred embodiment of=the invention, electric drive 22 holds the field current I, in motor 50 constant for a desired armature current corresponding to a given position of power pedal 44. As motor speed and frequency increase above the base value F 1.0, the electric drive 22 of the preferred embodiment also holds the terminal voltage VT constant for a given power pedal position, thereby resulting in the net magnetic flux, as represented by variable (VT R,,I,,)/F decreasing very nearly inversely proportional to frequency F. These conditions are represented in FIG. 6 for rated armature current by the vertical line at I,= 2.5 designated constant I for I 1.0, and it will be noted that the variable (VI I,,R,,)/F decreases from a value of 1.0 at frequency F 1.0 along this constant field current line to a value of 0.5 at frequency F= 2.0 and then decrease further to a value of 0.2 at F 5. Below frequency F 1.0, the terminal voltage VT is reduced by electric drive 22 as described hereinafter but at a rate that results in the net flux rising to a maximum as the frequency approaches zero. With the field current I, and terminal voltage VT constant, the armature current 1, is close to rated value (1,, 1.0) and the power factor close to unity over the entire range of frequency, thereby resulting in the electric drive system 10 having the hyperbolic constant power speed-torque characteristic shown in FIG. 5. Assuming that electric drive system 10 is designed to have a power rating matching that of diesel engine 20, this speed-torque curve of FIG. Smight alternatively be designated maximum electric drive system continuous capability. When less than rated power is required to drive the load and power pedal M is not fully depressed, the speed-torque characteristic may be represented by the dotted line curve designated reduced power" in FIG. 5.

Electric drive 22 regulates the terminal voltage VT applied to armature winding 54 of electric motor 50 as described above and also shifts the applied terminal voltage VT through the required phase angle relative to the angular position of the rotor to obtain the constant power torque'speed characteristic shown in FIG. 5. Such required phase angle is best described by reference to FIG. 7a, which shows the simplified equivalent circuit of synchronous motor 50 under steady state conditions, and to FIGS. 7b and which show its vector diagram for motor and generator operation respectively and wherein:

E is the internal voltage proportional to the field current; X, is the effective synchronous reactance for all field positions relative to the armature m.m.f.; and R, is the effective armature resistance. The armature current I results from the vector voltage difference acting on the machine impedance, and

thus:

FIG. 7b illustrates the vector diagram of this relationship for motor operation approximating the conditions in electric drive 22 at rated load for speed F 1.0, and FIG. 70 illustrates the vector diagram for generator operation approximating the conditions in electric drive 22 at speed F 1.0, with braking power less than rated load. The displacement angle DT is the phase angle between the internal voltage E and the terminal voltage VT applied to stator winding 54.

Electric drive 22 advances the terminal voltage VT in phase by the angle (+)DT relative to the physical axis of the internal voltage E on the rotor in order to produce the conditions for motor operation illustrated in FIG. 7b, and it delays the terminal voltage in phase by the angle (-)DT relative to the physical axis of E in order to provide the conditions for generator action shown in FIG. 70.

In the equivalent circuit and vector diagram of FIG. 7, the internal voltage E and effective synchronous reactance X, are proportional to frequency and are multiplied by F for operation at other than base frequency F 1.0.

FIG. 8 illustrates the terminal voltage VT and displacement angle DT which electric drive 22 applies to stator winding 5d of synchronous motor 50 at rated load to provide the desired constant power speedtorque characteristic of FIG. 5 with constant field current, essentially constant armature current and power factor close to unity. It will be noted that the displacement angle DT is 0 at F 0.0 and approaches at high frequency and motor speed. FIG. 8 shows only two VT curves designated rated power" and reduced power", but it will be appreciated that a different VT curve exists for each position of power pedal 44 and the corresponding power output level from motor 50.

Electric drive 22 includes a frequency changer, or cycloconverter 58 which is supplied with constant voltage, high frequency power from generator 30 over buses 38 and is responsive to gating signals from a firing circuit 60 to convert this high and constant frequency power to a lower variable frequency terminal voltage VT supplied over conductors 62 to stator phase windings 54X, 54Y and 542 of synchronous motor 50. Cycloconverter 58 is shown in detail in FIG. 14 and preferably includes a positive group of three thyristors,

or silicon controlled rectifiers associated with each of the three motor stator phase windings 54X, 54Y and 54Z to carry positive current from the three-phase power busses 38A, 38B and 38C and a negative group of three silicon controlled rectifiers associated with each of these three motor stator phase windings to carry negative current from the busses 38A, 38B and Firing circuit 60 derives gating signals which cyclically fire the silicon controlled rectifiers in cycloconverter 58 at desired points in the cycles of the high frequency, constant magnitude voltages A, B and C in busses 38A, 38B and 38C to generate the three-phase voltages in conductors L1, L2 and L3 which are applied to stator phase windings 54X, 54Y and 54Z.

Electric drive 22 includes a rotary inductor, vector adder, or resolver, termed angle sensor 64 driven by motor 50 for deriving a control signal for cycloconverter 58 which is a replica in magnitude, frequency and phase of the voltage VT (shown in FIG. 8) to be applied to stator winding 54 to obtain constant power over the speed range. In order to keep the poles generated in motor rotor 52'locked in with the revolving poles generated by motor stator winding 54, the frequency of the terminal voltage VT applied to stator winding 54 must at all times be in synchronism with rotor speed, and further the terminal voltage must be advanced in phase at all motor speeds by the displacement angle DT between the magnetic flux produced by the field current acting alone and the magnetic flux corresponding to the terminal voltage. Further, the magnitude of the terminal voltage VT impressed on stator winding 54 must be controlled as a function of motor speed in the manner shown in FIG. 8.

The variation in magnitude VT and phase angle DT of the terminal voltage shown in FIG. 8 to be applied to stator winding 54 can be expressed graphically by the loci of an equation in which motor speed is the variable parameter and the magnitude VT and phase angle DT are the radius vector and vectorial polar coordinates of the curve formed by the loci. FIG. 21 shows such a curve in dotted lines designated rated power plotting the loci of terminal voltage VT and phase angle DT when motor 50 is delivering rated power and also shows a curve in full lines designated reduced power. The magnitude of the terminal voltage VT to be applied to stator winding 54 as a function of motor speed is the radius vector of such curve, two such vectors V'Il and VT2 for the reduced power curve being shown in FIG. 21. The displacement angle by which the terminal voltage is to be advanced in phase relative to the rotor poles as a function of motor speed is the vectorial angle of the curve, two vectorial angles DTl and DT2 for the reduced power curve being shown. It will be noted that the magnitude of the terminal voltage VT is maintained constant from the base speed F 1.0 at the lower limit of the speed range (shown by vector VTl having phase angle DTl) with increase in motor speed, while the displacement angle increases from approximately 40 at F 1.0 to approximately 90 at speed F 3.5, at which the terminal voltage is shown by the radius vector VT2 and the displacement angle by the vectorial angle DT2.

A plurality of different curves can be plotted in FIG. 21 all of which are of the same shape and each of which represents a different position of power pedal 44 and a corresponding different power output level from motor 50. Each curve shown in FIG. 21 can also be defined by its rectangular coordinates x and y which vary as a function of motor speed F, or by the parametric equations of the curve having motor speed F as the variable parameter. Electric drive 22 includes an angle sensor control 76 which generates a pair of sine and cosine signals V and V representative of the y 'and x rectangular coordinates of a curve of FIG. 21 for each position of power pedal 44, and angle sensor 64 vectorially adds such signals and derives an output signal for controlling cycloconverter 58 whose magnitude and phase are in accordance with the radius vector and vectorial angle polar coordinates of such curve. Inasmuch as a curve of FIG. 21 is the loci of an equation which expresses the desired variation in magnitude VT and phase angle DT with motor speed as shown in FIG. 8, the terminal voltage VT applied by cycloconverter 58 to motor stator winding 54 is in accordance with one of the curves of FIG. 8 corresponding to a given power pedal position. As explained in detail hereinafter, the output signals from angle sensor 64 regulate firing circuit 60 which derives the gating signals for firing the thyristors of cycloconverter 58.

Rotary inductor, vector adder, or angle sensor 64 in effect converts the signals V and V representative of the y and x rectangular coordinates of a curve of FIG. 21 into the polar coordinates of such curve. Angle sensor 64 has a secondary winding 66 comprising three Wye-connected secondary phase windings 66X, 66Y and 66Z displaced 120 degrees (electrical) and a pair of energizing, or primary windings, termed sine winding 68 and cosine winding 70, displaced 90 electrically from each other magnetically coupled with secondary winding 66. The primary windings 68 and 70 and the three phase secondary windings 66X, 66Y and 662 are wound on an angle sensor stator 72 (see FIGS. 2, 3 and 4) mounted on the housing of motor 50, and the magnetic flux linkage between the secondary winding 66 and the primary windings '68 and 70 depends on the air gap between the stator 72 and a ferromagnetic rotor 74 connected to the motor rotor 52. The angle sensor rotor 74 is contoured to produce an approximately sinusoidal variation in the air gap and in the flux linkage between each secondary phase winding 66X, 66Y and 66Z and the primary windings 68 and 70 as it rotates.

The sine and cosine primary windings 68 and 70 are separately excited with high frequency, in-phase sine and cosine signals V, and V from angle sensor control 76 which are in accordance with the y and x rectangular coordinates respectively of a curve of FIG. 21 corresponding to a given position of power pedal 44. If motor 50 is at standstill and the angle sensor control 76 were to energize the sine and cosine windings with fixed magnitude, in-phase, high frequency alternating signals, the displaced sine and cosine windings 68 and 70 would have constant ampere turns and induce fixed magnitude, high frequency signals in the threephase secondary windings 66X, 66Y and 662. The permeances of the paths for the magnetic flux generated by the sine and cosine windings 68 and 70 and the voltage level of the fixed amplitude signals induced in the three-phase secondary windings is a function of the position of angle sensor rotor 74. When motor 50 rotates, the high frequency angle sensor output voltages induced in secondary windings 66X, 66Y and 662 are no longer fixed in amplitude but rather have a sinusoidal modulation at a relatively low frequency which is representative of the speed of the motor 50. The envelopes of the three angle sensor output signals induced in the secondary phase windings 66X, 66Y and 662 are displaced 120 (electrical because of the physical location of these windings on the angle sensor stator 72.

The term output voltage is used herein to connote either the carrier frequency signals induced in secondary phase windings 66X, 66Y and 662, their low frequency sinusoidal modulation envelopes, or the signals derived therefrom by demodulation to remove the carrier frequency and alternate half waves. The carrier frequency signals induced in secondary phase windings 66X 66Y and 662 are designated vt, and their low frequency modulation envelopes and the signals derived therefrom by demodulation are designated VT,,. Further, all three such forms of output voltage are directly proportional in magnitude, and their magnitude is represented in curves by the designation VT,.

Angle sensor control 76 receives a reference power signal from protection and regulation circuit 78 (see FIG. 1) which is a function of the position of power pedal 44 and independently controls the signals V, and V to sine and cosine windings 68 and 70 of angle sensor 64 as a function of this power signal, thereby controlling the ampere turns of these windings and the magnitude of the signals vt, (and their modulation envelopes VT,) induced in secondary phase windings 66X, 66Y and 662 which, after demodulation, control cycloconverter 58. Thus angle sensor control 76 suitably regulates the magnitude of the signals V, andV to the sine and cosine windings 68 and 70 of the angle sensor 64 to control the magnitude of terminal voltage VT applied to the motor stator winding 54 as a function of power pedal position. Change in position of power pedal 44 varies the magnitude of the power signal and thus changed the length of the radius vector VT in FIG. 2B.

Angle sensor control 76 also receives a speed" signal from tachometer 80 (see FIG. ll) which is a function of the speed of the motor 50 and modifies the signals V, and V to the sine and cosine windings 68 and 70 in response to the speed signal in accordance with the y and x rectangular coordinated of a curve of FIG. 21 so that the angle sensor output voltages VT, induced in secondary windings 66X, 66Y and 662 vary linearly (see FIGS. 8 and l 1) from zero at zero speed to full value (corresponding to a given position of power pedal 44) at base frequency F- 1.0 and remain at full value from F 1.0 to maximum motor speed F= 15.0 Above base speed F 1.0, angle sensor control 76 unequally varies the magnitude of the signals V, and V to the sine and cosine windings 68 and 76 in opposite directions as a function of motor speed (see FIG. III) while maintaining the magnitude of the angle sensor output voltage VT, constant for a given power pedal position, thereby unequally varying the ampere turns and the intensity of the magnetic flux which these windings 68 and 70 generate and shifting the phase of the modulation envelopes VT, of the angle sensor outill put voltages induced in secondary windings 66X, 66Y and 662 relative to the angular position of the angle sensor rotor 74 while maintaining the magnitude of these voltages constant. The output signals VT, from angle sensor secondary winding 66 control cycloconverter 58, and angle sensor control 76 thus regulates the displacement angle DT of the voltage VT applied to motor stator winding 653 relative to the magnetic poles on motor rotor 52 as a function of motor speed, while maintaining the magnitude of the terminal voltage VT constant for a given position of power pedal 44, by independently varying the magnitude of the sine and cosine signals V and V to sine and cosine windings 68 and to obtain the terminal voltage versus speed and displacement angle versus speed characteristics designated VT and DT in FIG. 8.

The three-phase carrier frequency output voltages vl, from angle sensor secondary windings 66X, 66Y and 662 are demodulated in a descriminator 82 to remove the carrier signal. Discriminator 82 provides three-phase output voltages VT of motor frequency controlled in magnitude and phase angle relative to a reference axis or the motor rotor, i.e., the axis of internal motor voltage E shown in the vector diagram of FIG. 7b.

The peak voltages of the low frequency output signals VT, from discriminator 82 are limited in a clipping circuit 84 which derives flat-topped output signals VT, (see FIG. 12) when the voltages from the discriminator 82 exceed the clipping level.

When the speed of motor 50 can be regulated over a speed range wherein the motor frequency voltages VT, applied to stator winding 54 vary from zero to fI-Iertz, the generator 30 provides voltages A, B and C having a frequency of at least 2f and preferably 3f when diesel 20 is controlled by its governor to run at top speed.

In order to condition the generator high frequency, constant magnitude voltages A, Band C in the busses 38A, 38B and 38C for generating the synchronizing, or sequence" signals required by firing circuit 60, a filter 86 (see FIG. ll) removes the commutation notches and high frequency noise from the generator voltages A, B and C and regulates the voltage level thereof to derive reference voltages which are reproductions of the fundamental waves of these generator voltages. Firing circuit 60 combines these three-phase, high frequency output reference" signals from filter 86 with the three-phase low frequency control signals VT, from clipping circuit 84 (which are proportional to the angle sensor output voltages VT,,) to derive the sequence" signals A+VT,, B+VT, and C+VT,, shown in FIG. 15c, and the firing circuit 60 includes level detectors (described hereinafter) which sense the zero crossing points of such sequence signals and generate the gating signals for the controlled rectifiers of the cycloconverter 53.

As explained hereinbefore, the terminal voltages VT applied to stator winding 54 and displacement angles D'I shown in FIG. 8 will result in the desired speedtorque characteristic of FIG. 5 with constant field current, essentially constant armature current, and power factor close to unity. Voltage drops occur in generator 30 because of the commutating inductance, and additional resistance and reactance voltage drops occur in the controlled rectifiers and center tapped reactors of 

1. In combination, a vehicle having a pair of tractive elements, steering means for turning said tractive elements relative to said vehicle to turn said vehicle, a prime mover on said vehicle, alternating current electric generator means on said vehicle driven by said prime mover, a pair of alternating current electric motors on said vehicle energized from said electric generator means and each having a stator winding and a rotor operatively connected to one of said tractive elements, turn compensation means controlled by said steering means for deriving a pair of turn compensation signals of opposite polarity for increasing and decreasing respectively the electrical power delivered by said generator means to said motors having rotors coupled to the outside and inside tractive elements on a turn, means for selectively deriving a power signal which is a function of the desired tractive effort of said vehicle, and a plurality of control means, each of which is between said electric generator means and one of said stator windings, for regulating the voltage from said generator means applied to said one stator winding as a function of both said power signal and one of said turn compensation signals and increasing said voltage in response to one polarity of turn compensation signal and decreasIng said voltage in response to the opposite polarity of turn compensation signal, said turn compensation means supplying said one and said other polarity of turn compensation signal to the control means for the motors of the tractive elements on the outside and inside of the turn respectively.
 1. In combination, a vehicle having a pair of tractive elements, steering means for turning said tractive elements relative to said vehicle to turn said vehicle, a prime mover on said vehicle, alternating current electric generator means on said vehicle driven by said prime mover, a pair of alternating current electric motors on said vehicle energized from said electric generator means and each having a stator winding and a rotor operatively connected to one of said tractive elements, turn compensation means controlled by said steering means for deriving a pair of turn compensation signals of opposite polarity for increasing and decreasing respectively the electrical power delivered by said generator means to said motors having rotors coupled to the outside and inside tractive elements on a turn, means for selectively deriving a power signal which is a function of the desired tractive effort of said vehicle, and a plurality of control means, each of which is between said electric generator means and one of said stator windings, for regulating the voltage from said generator means applied to said one stator winding as a function of both said power signal and one of said turn compensation signals and increasing said voltage in response to one polarity of turn compensation signal and decreasIng said voltage in response to the opposite polarity of turn compensation signal, said turn compensation means supplying said one and said other polarity of turn compensation signal to the control means for the motors of the tractive elements on the outside and inside of the turn respectively.
 2. In the combination of claim 1 wherein said turn compensation means increase and decrease said electrical power to said motors as a function of the angle through which said tractive elements are turned relative to said vehicle.
 3. In the combination defined by claim 2 wherein said vehicle has front and rear tractive elements on each side of the vehicle and an electric motor for each tractive element energized from said electric generator means and having its rotor operatively connected to said tractive element and wherein said steering means turn said front tractive elements and said turn compensating means increase the electrical power delivered by said generator means to the motors coupled to the front and rear tractive elements on the outside of the turn and decrease the electrical power delivered by said generator means to the motors coupled to the front and rear tractive elements on the inside of the turn as a function of the angle through which said front tractive elements are turned relative to said vehicle.
 4. In the combination of claim 1 wherein said turn compensation means varies the magnitude of said turn compensation signals as a function of the angle through which said tractive elements are turned relative to said vehicle and said control means vary said voltages applied to said stator windings as a function of said magnitude of turn compensation signals.
 5. In the combination of claim 4 wherein said turn compensation means control the magnitude of said turn compensation signals as a function of both the angle through which said tractive elements are turned relative to said vehicle and the magnitude of said power signal.
 6. In the combination of claim 4 wherein said vehicle has front and rear tractive elements on each side of said vehicle and an electric motor for each tractive element having a stator winding and its rotor operatively connected to said tractive element and wherein said steering means turn said front tractive elements relative to said vehicle and including one of said control means for each said motor and wherein said turn compensation means supply said one and said other polarity of turn compensation signals to the control means for the motors for both front and rear tractive elements on the outside and the inside of the turn respectively and increase and decrease the magnitude of said turn compensation signals as a function of the angle through which said front tractive elements are turned relative to said vehicle.
 7. In the combination of claim 4 and including means associated with each side electric motor for deriving a speed signal which is a function of motor speed and wherein each said control means regulates the magnitude and shifts the phase of the voltage applied to the associated motor from the associated electric generator means as a function of said speed signal and said power signal and said turn compensation signal.
 8. In combination, a vehicle having a plurality of tractive elements, a plurality of electric motors on said vehicle each having a polyphase stator winding and a rotor operatively connected to one of said tractive elements, a prime mover on said vehicle, polyphase electric generator means on said vehicle driven by said prime mover, a plurality of means each of which is associated with one of said motors operatively connected to said rotor for deriving an output signal having a frequency which is a function of the speed of said motor, a plurality of polyphase frequency converters each of which is connected between said electric generator means and the stator winding of one of said motors controlled by said output signal which is a function of the speed of said one motor, a plurality of control means each of which is associated with one of said motors for varying a condition of said output signal, steering means for turning a pair of said tractive elements relative to said vehicle to steer said vehicle, and turn compensation means controlled by said steering means and coupled to said plurality of control means for increasing the magnitude of said output signal supplied to the frequency converter of the motor coupled to the outside tractive element on a turn and for decreasing the magnitude of said output signal supplied to said frequency converter of the motor associated with the inside tractive element on the turn.
 9. In the combination of claim 8 wherein said turn compensation means varies the magnitude of said output signals to the frequency converters for the motors coupled to the outside and inside tractive elements as a function of the angle through which said tractive elements are turned relative to said vehicle.
 10. In the combination of claim 9 wherein said vehicle has a pair of said tractive elements on each side thereof and said turn compensation means increases the magnitude of said output signals to the frequency converters of the motors coupled to said pair of tractive elements on the outside of a turn and decreases the magnitude of said output signals to said frequency converters of the motors coupled to the pair of tractive elements on the inside of a turn as a function of the angle through which said pair of tractive elements are turned relative to said vehicle by said steering means.
 11. In the combination of claim 9 and including means for selectively deriving a power signal which is a function of the desired tractive effort of said vehicle, and wherein said turn compensation means derives a pair of turn compensation signals of opposite polarity and each of said control means regulates said output signal as a function of both said power signal and one of said turn compensation signals.
 12. In the combination of claim 11 wherein said turn compensation means varies the magnitude of said turn compensation signals as a function of both said power signal and the angle through which said tractive elements are turned relative to said vehicle. 